1. Field of the Invention
The present invention relates to conveyance roller structures, in general, and to rollers for supporting and guiding metallic workpieces during heating within a furnace, in particular.
2. Description of the Prior Art
In the past, roller-type hearths have been provided in furnaces to support numerous different forms of work-pieces as, for example, a plurality of bars or slabs during heating within the furnace. Heavy metallic slabs have been heated by conveying them through successively arranged furnaces or tandem heating zones within one or more furnaces. Such workpieces are heated for a number of different reasons, all of which usually are characterized by the need to supply heated workpieces from the furnaces at a uniform temperature. The actual temperature to which these workpieces are heated depends upon the particular metalworking or treating operations but, generally, the workpieces are raised to a temperature above the critical temperature of the metal and frequently it is desired to raise the temperature of the workpiece to 2,000.degree. F. or higher.
In some heating furnace designs, water-cooled skids are used to support the workpiece during heating. The results, however, are undesirable because pronounced cold spots are formed at each area where the workpiece was supported on the skids. This is particularly undesirable where the workpieces are heated prior to quenching, rolling, leveling and other processing operations involving metal deformations. There are other forms of furnace hearths known in the art which involve the use of rollers to support the workpiece. These rollers are typically constructed through the use of a tri-union mounted to the ends of an alloyed tube forming the roller body. The temperature of the roller is increased in essentially the same manner as the workpiece supported thereby during heating.
An improved version of such rollers is disclosed in U.S. Pat. No. 3,860,387. As disclosed therein, the roller comprises a central, axially-extending, fluid-cooled arbor surrounded by an outer tubular sleeve member which is in contact with the workpieces being heated. There is an annular space between the outer periphery of the arbor and the inner periphery of the sleeve. In this space are arcuate segments for supporting the sleeve on the arbor without materially transmitting heat from the hot outer tubular sleeve to the inner fluid cooled arbor. That is, the arcuate segments provide sufficient structural support for the outer, hot sleeve which may be at a temperature of at least 2,000.degree. F. and the inner, much cooler fluid-cooled arbor such that the arbor does not act as a heat sink so as to produce cold spots on the outer periphery of the annular sleeve which would deleteriously affect the characteristics of the workpiece being heated.
Such a roller is useful for preventing unwanted cold spots on workpieces which are heated in the furnace. However, such a design provides no means for positively guiding or tracking a plate-like workpiece as it passes through a furnace. Without means for positively guiding a workpiece through the furnace, the workpiece may bump the walls of the furnace or even become jammed therein. Obviously, such bumping or jamming of the workpiece within the furnace may produce damage to the workpiece and/or the furnace which oftentimes requires a shutdown operation to remove the workpiece from the furnace. Such shutdowns are costly and inefficient work stoppages and are sometimes of rather great duration if significant maintenance is required to repair a damaged furnace. Therefore, other guide means must be provided to positively guide the workpiece through the furnace.
Unfortunately, however, additional guide means add undesirable cost increased heat loss and complexity to the furnace design. And even when equipped with such guides means, such a system is limited in the thickness of workpiece it can accommodate. Such a system can only be effectively used on thick workpieces having a high degree of structural integrity, i.e., workpieces which will not become too soft and then become damaged through contact with guide means within the furnace. And, as can be appreciated, the greater the thickness of the workpiece, generally the more treatment is required to reduce the workpiece to a final thickness--especially if the workpiece is to be formed into thin coiled steel strip. For obvious reasons, greater thickness rolling reductions of the workpiece add to the manufacturing cost and time required for forming the final product.
Flexible roller designs have been introduced for guiding a metallic strip workpiece as it is conveyed through the various "unheated" workstations of a production plant. Such roller designs advantageously eliminate the need for additional workpiece guide means structure to be provided. However, such designs are of no use in a high-heat furnace environment since they are formed of materials which will become severely damaged if not completely destroyed under the extreme heat conditions experienced within a furnace. Examples of such "self-centering" strip rollers are disclosed in U.S. Pat. Nos. 2,592,581--2,660,429 --2,720,692 and 2,772,879. Each of these patents, with the exception of U.S. Pat. No. 2,660,429, disclose roller structures formed of rubber, leather, fabric or other resilient material which would be destroyed by the roughly 2,000.degree. F. temperature produced within the heating and soaking furnace of a rolling mill production plant. U.S. Pat. No. 2,660,429 discloses an embodiment of a roller having a series of axially-spaced webs projecting from an arbor structure. However, if such a roller structure were to be subjected to the heat produced within a heating and soaking furnace and the constant weight of metallic workpieces, the laterally unsupported webs as well as the arbor will be subject to accelerated creep and permanent distortion.
An advantage exists, therefore, for a flexible conveyance and guidance roller structure for use in furnaces which avoids the creation of undesirable cold spots on the surface of a workpiece being heated while at the same time positively guides through the furnace--without any additional guide means--a class of thin, flexible and wide workpieces having little inherent structural integrity which heretofore could not be effectively passed through a furnace. With the provision of a system of such roller structures, which have particular use with thin continuously--cast plate or strip, significant reductions in cost and time are achieved in producing the final product. Still further, such a system will simplify and revolutionize the design and reduce the cost of construction of reduction mills by eliminating the need for a number of the roughing and/or finishing trains required to work a workpiece to a final product thickness.
It is therefore an object of the invention to provide an improved roller structure for positively guiding and conveying workpieces through a furnace.
It is a further object of the invention to provide a flexible roller structure for guiding and conveying workpieces through a furnace without the need for additional guide means.
It is a further object of the invention to provide a roller structure for guiding and conveying thin workpieces having little inherent structural integrity through a furnace.
It is a further object of the invention to provide a roller structure for imparting negligible cold spot areas to workpieces being heated as the workpieces are passed through a furnace.
It is yet a further object of the invention to provide a furnace roller structure which is of simple and inexpensive construction.
It is a further object of the invention to provide a system of workpiece guidance and conveyance roller structures for permitting a reduction in cost and time in producing a final workpiece product.
It is still a further object of the present invention to provide a roller structure system for permitting simplification of the design and a reduction in the construction cost of a reduction mill.
Still other objects and advantages will become apparent in light of the attached drawing figures and written description of the invention presented hereinbelow.